Over the past decade there has been a significant increase in the concern for fire safety in the home. This is particularly evidenced by an increased awareness and interest in fire safety devices for use in the home; such as fire ladders, fire extinguishers and smoke alarms.
Consistent with the increased concern for fire safety is the imposition by Underwriters Laboratories, Inc. of more stringent thermal requirements for pan-type lighting fixtures. In particular, U/L 57Standard for Electric Lighting Fixtures dated Jan. 13, 1978, sets forth stringent temperature limits which cannot be exceeded if U/L approval is to be obtained.
Section 27.3 of U/L 57 states:
TEMPERATURE LIMITS--A fixture subjected to a temperature test shall not cause temperatures to exceed values specified in paragraph 27.4. PA1 60.degree. (140.degree. F.) at any point within a fixture wiring box or compartment, or if the fixture is to be mounted to an outlet box, at any point the supply wire could normally contact (the supply wire inside the outlet box is 6" in length).
The instant invention primarily is concerned with the requirements set forth in the first sentence of 27.4B, which provides as follows:
Pan-type fixtures must meet the above temperature requirements in order to receive U/L approval for use in houses wherein the wiring does not justify a higher temperature rating; which is commonly the case in older homes.
It is known in the prior art to employ a heat dissipating material such as aluminum in lighting fixtures and appliances. This is evidenced by U.S. Pat. No. 4,107,768, issued to Lemkin (note the aluminum ring D of light bulb globe A); U.S. Pat. No. 3,461,283, issued to Hahn (note the cast aluminum housing 10 of the vandalproof luminary); U.S. Pat. No. 3,869,606, issued to Fordsmand (note housing 10 of the fluorsecent unit); U.S. Pat. No. 3,348,036, issued to both Bodian et. al, (note metal frame 41 of the examination light) and U.S. Pat. No. 3,560,728, issued to Atkin (note hollow conical housing 11 of the floodlight).
Although all of the above patents disclose the use of aluminum as a heat dissipating material in lighting devices, the use of such a material by itself in forming the base of a pan-type fixture will not provide the necessary heat insulating characteristics to meet the above-discussed U/L requirements.
It is generally desirable to employ a central, threaded mounting stud to mount a pan-type fixture on the ceiling in association with an outlet box. This is evidenced by U.S. Pat. Nos. 1,825,920, issued to Popp; 1,600,639, issued to Williamson; 1,906,197, issued to Mangin; 1,155,350, issued to Gilson et. al. and 4,044,246, issued to Docimo et al. Prior to this invention all of the studs employed to mount pan-type fixtures, to the best of applicant's knowledge, have been of a metal, heat conductive material. None of the above petents suggest the use of any other type of material for such a stud, and a pan-type fixture employing a metal mounting stud will not meet the U/L requirements set forth in Section 27.4B, 1st sentence.